1. Field of the Invention
The present invention relates to a suspension device provided in an automotive seat, and in particular is directed to an improvement in the suspension device for automotive seat, which comprises a hydraulic damper with a coil spring wound therearound in order to adjust the cushionny effect according to a weight of an occupant on the seat.
2. Descrition of Prior Art
Typically, some of the hitherto suspension devices are of such a construction including an upper frame on which a seat cushion is mounted and a lower frame fixed on the floor side of the automobile, with an X-shaped link being movably interconnected with both of the upper and lower frames, so that the upper frame may be vertically move relative to the lower frame, wherein a hydraulic damper is interposed between the two frames for absorbing vibrations and rolling applied to the seat. In particular, there are a seat suspension device in which the hydraulic damper is provided with a compression coil spring therearound, which is adjustable in elastic reperecussion force at a proper degree matching to a particular weight of occupant sitting on the seat.
In this kind of suspension device, an upper annular support ring and a lower annular ring are provided at the respective upper and lower ends of the compression coil spring, such that the upper ring is disposed at the upper frame, whereas the lower ring is secured at the hydraulic damper, whereby the spring is adjusted in repercussion force by contracting and expanding the spring thus sandwiched between the upper and lower support rings, so as to permit adjustment of such spring repercussion force according to the occupant's weight.
Specifically stated, in a typical adjustment mechanism of this particular suspension device, a cam is rotatably attached about a cylinder of the hydraulic damper for contact with a stopper provided thereon, and the foregoing lower support ring is fixed integrally with the upper edge of the cam. The lower annular edge of the cam is formed unevenly to present certain undulations or irregularities for a proper adjustment purpose, and the stopper is fixed on the outer surface of the cylinder for contact with such undulations. The cam is, at its outer peripheral surface, formed with a plurality of equidistant cylindrical insert parts for receipt of a rod-like jig for causing the cam to be rotated. In operation, the forward end of the jig is inserted into one of insert parts, and the jig is rotated in a direction circumferentially of the cylinder, with the result that the cam is rotated, causing vertical displacement of the lower support ring in accordance as the undulated cam surfaces of the cam rides on and along the end of stopper. Such vertical displacement of the lower support ring produces adjustable variations in spacing between the lower and upper support rings, to thereby increase and decrease the repercussion force of the abovementioned coil spring, whereby an occupant can adjust the cushiony conditions or height of the seat at an optimal degree matching to his or her weight.
However, the foregoing adjustment of the spring in repercussion force has to be made by use of a jig for insertion into the insert portions of cam, which results in a poor operation of the suspension device, and further in making it rather hard for an occupant to finely adjust the springs' repercussion force.
Furthermore, the occupant has to adjust the spring's repercussion force, after having bending his body forwardly while sitting on the seat, for access to the operation knob disposed under the seat cushion. As a result, his or her weight at normal sitting posture becomes different from that at such forwardly bending posture, and consequently, the weight is not fully imparted to the compression coil spring, which prevents the occupant from making a precise adjustment for the repercussion force, according to his and her weight.